The flat belts of this kind comprise an elastomeric material wherein tension carriers in the form of steel cords or plastic cords are integrated. In the manufacture of flat belts of this kind, one strives to position the cords in a single plane which is the bending-neutral plane.
(1) For positioning the cords exactly, the so-called winding-projection method has proven to be especially suitable. For this purpose, the mold drum used for manufacture is provided with (transverse) ribs, so-called projections. The upper edge of these ribs determines the plane of the cords. The ribs (projections) generate slots in the belt surface congruent thereto. The winding-projections technology is, for example, known from the manufacture of toothed belts (see, for example, U.S. Pat. Nos. 3,880,558 and 4,268,471).
In the area of elevator technology too, an exact positioning of the tension carriers results (see, for example, DE 25 12 530 A1) which are produced with the aid of winding-projection mold drums.
With the use of winding-projection mold drums for flat belts in elevator technology, other disadvantages have, however, crept in: these are the noise development given by the slot frequency and the increased bending load in the region of the slots.
(2) Flat belts with a noise-reduced groove arrangement are suggested for reducing the load given by the slot frequency. The grooves (slots), which are described in the European patent Publication EP 1,353,087 and United States patent application publication US 2006/0175137, are not at right angles but are preferably aligned to be inclined. They can be in straight lines, bent or be configured to have a V-shape or a zigzag-shape. Furthermore, the grooves can be spaced differently one from the other.
Flat belts, which are to be built into elevator systems, are redirected in both directions while running over various sheaves. For this reason, the plane of the reinforcement carriers should be arranged centrally in the belt. However, even when the tension carriers described are arranged centrally within the belt, a different bending characteristic results already on both sides because of the slots and this bending characteristic comes with an increased bending load in the region of these slots.
(3) To eliminate this unwanted condition, U.S. Pat. No. 6,966,763 suggests a two-stage method for manufacturing flat belts provided with reinforcement carriers. In these belts, there is likewise a planar positioning of the tension carriers parallel to the running surface. Because no slots are present here which are generated by winding projections, a longer service life can be anticipated because of the more uniform tension distribution.
Furthermore, this elevator belt is characterized by a very high cord density. In the semi-product, approximately half of the tension carrier cross section is exposed. The PU (polyurethane elastomer) surface on this belt side is therefore relatively small. To this side, however, the second belt half must be bonded in the second process step. The PU of the second belt half must then be welded to the PU of the first belt half.
The disadvantage of this belt, which is produced in the two-stage method, is given by the relatively small PU surface at the belt side which is to be welded. This disadvantage lies in a theoretical layer separation. The belt half, which is applied in the second step would again separate, and the tension carriers could come into direct contact with the drive discs. Furthermore, this method has the disadvantage that the bonding of the belt material to the tension carriers is not optimal.